The use of air-filled envelopes, cushions, and pillows (herein collectively referred to as "inflatables") for packaging and shipping has, in the past 10 years, become reality through the use of thin film plastics which are inexpensive, tough, resilient, and recyclable. Such inflatables are created using heat sealed bags from these plastic films and can be advantageously used for void-fill packaging to replace products such as crumpled paper or polystyrene peanuts and for protective packaging to replace products such as molded or extruded foams. Overall, inflatables offer cost advantages over conventional materials because of their minimal storage volume and inherent minimal material usage.
The difficulties in creating inflatable packaging are generally related to the inflation process. In accordance with the conventional technique, two layers of the plastic film are formed together as tubing which is then divided into sections to create individual bags that must be inflated at the user site. The air must be sealed shut within the bag. Conventionally, this is accomplished by using valves or by heat sealing the plastic tubing during inflation. Inherently, this inflation process is slow and causes intermittent production of the air-filled bags or pillows rather than continuous production.
In accordance with one prior art technique, the inflation for each bag is accomplished by inserting air nozzles or needles into the plastic substrate of the material or into the valves. The step of inserting the air nozzle or needle into the substrate material or valving for each individual bag requires that the bags be stationary for best results. This adds complexity to the machine and reduces the robustness of the inflation system. In addition, the time cycle associated with the inflation process can be on the order of 2 to 10 seconds and this adds additional production delay. Furthermore, it is difficult to insert a needle into the valve or through the wall of the flexible tubing without pricking the tubing material a second time. A machine and method which eliminates the use of air nozzles and needles for pressurizing inflatable packages and which further allows for continuous production of several air-filled bags simultaneously would constitute a significant advance in the art.
Once the inflatable bag has been pressurized with air, the bag must be sealed to capture the pressurized air in the bag. In accordance with one conventional technique, one way valves, such as those described in U.S. Pat. No. 5,755,328, are used to keep air inside the inflated bag. However, such valves are prone to leakage problems. Moreover, the use of valves add significantly to the cost to produce each bag. In addition, both flutter valves and solid rigid valves, because of their thickness, tend to complicate and inhibit the compact folding or roll-up capability of the deflated end-to-end packages such as those disclosed in U.S. Pat. No. 5,454,642. Accordingly, a machine and method which allows for the continuous production of inflatable packages from a compact roll of adjacent and connected deflated inflatable preformed plastic film material would be desirable.
One alternative to using valves in the inflatable bags is to heat seal the upper and lower film layers of the preformed bag together so that the air is trapped within the bag to form the inflated package. In general, the process of heat sealing bags is time consuming and requires a minimum of 1 to 2 seconds to accomplish for polyethylene based films of thicknesses ranging from 0.001 to 0.003 inches. In addition, the handling and positioning of the film can require an additional 1 to 5 seconds. To the inventors' knowledge, techniques for heat sealing continuously moving polyethylene based films has not been perfected for inflatable packaging applications. One difficulty encountered in forming a heat seal in moving plastic sheet is maintaining the delicate balance of temperature, pressure and duration necessary to ensure a strong and reliable bond as the material is moving (often at variable speeds) relative to the heat seal apparatus. If the heating element is too hot or the applied pressure is too great, the plastic simply melts completely through or the seam rips open. If the heating element is not hot enough, the fuse area of melted plastic between the sheets to be joined does not hold and the seam fails. Another factor which complicates the heat sealing process of moving plastic sheet material is the internal inflation pressure of the adjacent air filled cavity which has a tendency to pulls apart the newly heat sealed seam.
In order to reduce costs of packages, some systems avoid preforming the inflatable plastic bags prior to the customer end-use and instead use a single continuous sheet of plastic film that has been folded lengthwise with the edges joined together to form tubing from which bags are created at the time of need. The film is fed into a machine and divided into bag sections which are individually inflated and heat sealed perpendicularly to the length of the tubing thus creating a chain of inflated packets. Such systems are slow because they require individual inflation and heat sealing of each bag section perpendicularly to the direction of the movement of the film (tubing). In consequence, the film must either be stopped to heat seal it shut, or an oscillating sealing station must be used which moves in the direction of the film.
The present invention is directed to machine and method for the manufacture of a continuous production of pneumatically filled pillows from a strip of flattened preformed film material of adjacent and connected inflatable plastic pillow sections, wherein the individual pillows of the pillow sections are heat sealed in the same direction of movement of the film material in order to confine the gas therein.